1. Field of the Invention
The present invention generally relates to communication devices, and more particularly to a communication device which has a function of controlling a disconnection of a line which is being used for a communication when an abnormality is detected in a computer equipment which is coupled to the communication device.
2. Description of the Related Art
In a communication using a communication device such as a modem which is coupled to or built into a computer equipment, control related to disconnection of a line which is being used for the communication is in most cases carried out based on a signal received from the computer equipment. For this reason, if a failure or the like occurs in the computer equipment and a line disconnection instruction is not correctly issued from the computer equipment, the line remains in a connected state. When the line remains in the connected state, the accounting continues to be made with respect to the use of the line and the connection to a destination. Recently, there are more occasions to make a communication using a combination of the computer equipment, the communication device and a wireless telephone set. Consequently, in addition to the problem of the continued accounting being made when the failure is generated in the computer equipment, the wear of a battery of the wireless telephone set due to the continued communication is also becoming a problem.
With respect to the above described problems, a first method has been proposed to disconnect the line by detecting a no-communication state which is generated when an abnormality is occurs in the computer equipment. However, according to this first method, the no-communication state is not necessarily caused by the abnormality state of the computer equipment, and it is difficult to accurately detect the abnormal state of the computer equipment. As a result, there is a high possibility that an unwanted disconnection of the line will be made.
On the other hand, a second method has been proposed to transmit an exclusive control code with respect to the communication device when an abnormality is generated in the computer equipment. However, according to this second method, it is necessary to modify the hardware and software of the computer equipment from the existing hardware and software in order to generate the exclusive control code.
As described above, it is conventionally impossible to disconnect the line by accurately detecting the abnormal state of the computer equipment using a simple structure or, to disconnect the line by accurately detecting the abnormal state of the computer equipment without the need to modify the existing hardware and software of the computer equipment.